Ball bearing for use in vacuum and turbo-molecular pump incorporating same

Abstract

A ball ball bearing for use in a vacuum is a sealed full-type ball bearing comprising an inner ring and an outer ring both made of stainless steel, balls made of a ceramic composed primarily of silicon nitride, and stainless steel shield plates. The bearing has enclosed therein a grease of low-volatility composition comprising a diester synthetic oil serving as a base oil, an organic condensation agent and an ethylene tetrafluoride resin additive.

What is claimed is: 
     
       1. A sealed full-type ball bearing for use in a vacuum comprising an inner ring and an outer ring both made of stainless steel, balls mad of a ceramic composed primarily of silicon nitride, and stainless steel shield plates, the bearing having enclosed therein a grease comprising a diester synthetic oil serving as a base oil, and organic condensation agent and an ethylene tetrafluoride resin additive. 
     
     
       2. A turbo-molecular pump comprising a multiplicity of stationary blades provided inside a casing and arranged axially thereof, a rotary member supported inside the casing by ball bearings and rotatable by an electric motor, and a multiplicity of rotary blades mounted on the rotary member and facing the respective stationary blades axially of the member, the turbo-molecular pump being characterized in that each of the ball bearings supporting the rotary member is a sealed full-type ball bearing comprising an inner ring and an outer ring both made of stainless steel, balls made of a ceramic composed primarily of silicon nitride, and stainless steel shield plates, the bearing having enclosed therein a grease comprising a diester synthetic oil serving as a base oil, an organic condensation agent and an ethylene tetrafluoride resin additive.